1. Field of the Invention
The invention is related to the field of flow meters, and in particular, to flow meter electronics capable of outputting either a frequency output signal or a digital communication protocol signal over a single output port.
2. Statement of the Problem
Coriolis mass flow meters measure mass flow and other information with respect to materials flowing through a pipeline as disclosed in U.S. Pat. No. 4,491,025 issued to J. E. Smith, et al., of Jan. 1, 1985 and U.S. Pat. No. Re. 31,450 to J. E. Smith of Feb. 11, 1982. These flow meters typically comprise a flow meter electronics portion and a flow meter sensor portion. Flow meter sensors have one or more flow tubes of a straight or curved configuration. Each flow tube configuration has a set of natural vibration modes, which may be of a simple bending, torsional, radial, or coupled type. Each flow tube is driven to oscillate at resonance in one of these natural vibration modes. The natural vibration modes of the vibrating, material filled systems are defined in part by the combined mass of the flow tubes and the material within the flow tubes. When there is no material flowing through a Coriolis flow meter sensor, all points along the flow tubes oscillate with a substantially identical phase. As material flows through the flow tubes, Coriolis accelerations cause points along the flow tubes to have a different phase. The phase on the inlet side of the flow meter sensor lags the driver, while the phase on the outlet side of the flow meter sensor leads the driver.
Coriolis flow meter sensors typically include two pick-offs for producing sinusoidal signals representative of the motion of the flow tubes at different points along the flow tubes. A phase difference of the sinusoidal signals received from the pick-offs is calculated by the flow meter electronics. The phase difference between the pick-off signals is proportional to the mass flow rate of the material flowing through the flow meter sensor. An example of a Coriolis flow meter is described below in FIG. 1.
The flow meter electronics receive the pick-off signals from the pick-offs. The flow meter electronics process the pick-off signals to compute a mass flow rate, a density, or another property of the material passing through the flow meter sensor. The flow meter electronics typically have multiple output ports or multiple communication channels for outputting the mass flow rate, the density, or other information. For instance, typical flow meter electronics have a milliamp output, a discreet voltage output, a digital communications protocol output, and a frequency output. Each output has its own physical port. The flow meter electronics with multiple output ports provide a great deal of versatility to users, which can be useful for certain applications. Unfortunately, flow meter electronics with multiple output ports can be expensive and may have more functionality than is needed for simple applications.
To help solve this problem, less complex and cheaper flow meter electronics have been developed. The less complex flow meter electronics still receive the pick-off signals from the pick-offs, and process the pick-off signals to compute a mass flow rate, a density, or another property of the material passing through the flow meter sensor. The less complex flow meter electronics differ by having a single output port. The less complex flow meter electronics only generate a digital communication protocol signal that represents the mass flow rate, the density, or the other properties. Unfortunately, some users have legacy systems that are configured to receive a frequency or pulse signal and do not understand a digital communication protocol signal.
Traditionally, the flow meter industry mainly involves mechanical flow meters, such as positive displacement meters, oval gear, or turbine flow meters. These mechanical flow meters generate a pulse signal when the chamber, gear, or blade passes through a magnetic field, or from a magnetic rotating component on a shaft. Legacy systems receive the pulse signal and provide a read out of the flow rate, adjust a valve based on the flow rate, or perform another function. Newer electronic flow meters have also been configured to generate a pulse signal proportional to a flow rate to interface with these legacy systems. Unfortunately, no flow meter electronics have been developed that will interface with legacy systems and current flow systems, but are cost effective for less complex applications.
The invention helps solve the above problems with flow meter electronics that can be programmed to either output a frequency output signal or a digital communication protocol signal over a single output port. The invention advantageously provides flow meter electronics that are cheaper and better suited for less complex applications. The flow meter electronics are also capable of interfacing with legacy systems with the frequency output signal or interfacing with more modem systems with the digital communication protocol signal.
One embodiment of the invention includes flow meter electronics for providing a flow rate of a material flowing through a flow meter sensor of a Coriolis flow meter. The flow meter electronics comprise a processing system and a single output port. The processing system receives pick-off signals from the flow meter sensor and processes the pick-off signals to determine the flow rate of the material. The processing system receives an instruction for a frequency output signal or a digital communication protocol signal. If the instruction is for a frequency output signal, then the processing system processes the flow rate to generate a frequency output signal having a frequency proportional to the flow rate, and transmits the frequency output signal over the single output port. If the instruction is for a digital communication protocol signal, then the processing system processes the flow rate to generate a digital communication protocol signal that represents the flow rate, and transmits the digital communication protocol signal over the single output port.
In another embodiment, the processing system determines a direction of flow of the material. If the direction of flow is in a forward direction, then the processing system generates the frequency output signal to have a duty cycle below 0.5. If the direction of flow is in a reverse direction, then the processing system generates the frequency output signal to have a duty cycle above 0.5.
In another embodiment of the invention, the processing system determines if a fault has occurred. The processing system generates the frequency output signal having a predetermined frequency responsive to determining the fault.
The invention also includes other embodiments described below.
The following depict aspects of the invention. One aspect is flow meter electronics for providing a flow rate of a material flowing through a flow meter sensor of a Coriolis flow meter, said flow meter electronics comprising:
a single output port; and
a processing system coupled to said single output port and configured to:
receive pick-off signals from said flow meter sensor,
process said pick-off signals to determine said flow rate of said material,
receive an instruction for a frequency output signal or a digital communication protocol signal,
if said instruction is for said frequency output signal, then said processing system is further configured to process said flow rate to generate said frequency output signal having a frequency proportional to said flow rate, and transmit said frequency output signal over said single output port, and
if said instruction is for said digital communication protocol signal, then said processing system is further configured to process said flow rate to generate said digital communication protocol signal that represents said flow rate, and transmit said digital communication protocol signal over said single output port.
Preferably, the processing system is further configured to:
determine a direction of flow of said material;
if said direction of flow is in a first direction, then generate said frequency output signal to have a duty cycle below 0.5; and
if said direction of flow is in a second direction, then generate said frequency output signal to have a duty cycle above 0.5.
Preferably, the processing system is further configured to:
determine if a fault has occurred; and
generate said frequency output signal having a predetermined frequency responsive to determining said fault.
Preferably, the processing system is further configured to receive said instruction over said single output port from a user.
Preferably, the flow rate comprises a mass flow rate.
Alternatively, the flow rate comprises a volumetric flow rate.
Alternatively, the flow rate comprises a net volumetric flow rate.
Another aspect is a method of operating flow meter electronics for providing a flow rate of a material flowing through a flow meter sensor of a Coriolis flow meter, said method comprising the steps of:
receiving pick-off signals from said flow meter sensor;
processing said pick-off signals to determine said flow rate of said material;
receiving an instruction for a frequency output signal or a digital communication protocol signal;
if said instruction is for a frequency output signal, then processing said flow rate to generate said frequency output signal having a frequency proportional to said flow rate and transmitting said frequency output signal over a single output port; and
if said instruction is for said digital communication protocol signal, then processing said flow rate to generate said digital communication protocol signal that represents said flow rate and transmitting said digital communication protocol signal over said single output port.
Preferably, the method further comprises:
determining a direction of flow of said material;
if said direction of flow is in a first direction, then generating said frequency output signal to have a duty cycle below 0.5; and
if said direction of flow is in a second direction, then generating said frequency output signal to have a duty cycle above 0.5.
Preferably, the method further comprises:
determining if a fault has occurred; and
generating said frequency output signal having a predetermined frequency responsive to determining said fault.
Preferably, the method further comprises receiving said instruction over said single output port from a user.
Preferably, the flow rate comprises a mass flow rate.
Alternatively, the flow rate comprises a volumetric flow rate.
Alternatively, the flow rate comprises a net volumetric flow rate.
Another aspect is a software product for providing a flow rate of a material flowing through a flow meter sensor of a Coriolis flow meter, said software product comprising:
flow meter software configured when executed by a processing system to direct the processing system to receive pick-off signals from said flow meter sensor, process said pick-off signals to determine said flow rate of said material, receive an instruction for a frequency output signal or a digital communication protocol signal, process said flow rate to generate said frequency output signal having a frequency proportional to said flow rate and transmit said frequency output signal over a single output port if said instruction is for said frequency output signal, and process said flow rate to generate said digital communication protocol signal that represents said flow rate and transmit said digital communication protocol signal over said single output port if said instruction is for said digital communication protocol signal; and
a storage media configured to store said flow meter software.
Preferably, the flow meter software is further configured to direct said processing system to:
determine a direction of flow of said material;
if said direction of flow is in a first direction, then generate said frequency output signal to have a duty cycle below 0.5; and
if said direction of flow is in a second direction, then generate said frequency output signal to have a duty cycle above 0.5.
Preferably, the flow meter software is further configured to direct said processing system to:
determine if a fault has occurred; and
generate said frequency output signal having a predetermined frequency responsive to determining said fault.
Preferably, the flow meter software is further configured to direct said processing system to receive said instruction over said single output port from a user.
Preferably, the flow rate comprises a mass flow rate.
Alternatively, the flow rate comprises a volumetric flow rate.
Alternatively, the flow rate comprises a net volumetric flow rate.